Pension and Other Postretirement Benefits - Schedule of Fair Values of Other Postretirement Benefit Plans by Asset Category (Details) - USD ($) $ in Millions	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 112.8	119.0	$ 117.9
Other Benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	27.3	35.3
Other Benefits | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	85.5	83.7
Other Benefits | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	85.5	83.7
Other Benefits | Commingled funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Commingled funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Commingled funds | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	85.5	83.7
Other Benefits | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	27.1	27.1
Other Benefits | Short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	27.1	27.1
Other Benefits | Short-term investments | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Government agency bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.2	4.8
Other Benefits | Government agency bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Benefits | Government agency bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.2	4.8
Other Benefits | Government agency bonds | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0.0	0.0
Other Benefits | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		3.4
Other Benefits | Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0.0
Other Benefits | Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		3.4
Other Benefits | Corporate bonds | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		$ 0.0